1. Field of the Invention
The invention relates to a LED lamp and color mixing optics for illuminating a surface under a flat angle. The LED lamp produces a uniform intensity distribution and a uniform color output throughout the beam pattern of the light beam produced by a multi-color LED light source.
2. Description of Relevant Art
In linear lighting applications such as cove lighting and wall washing, it is desired to shape the beam of a lamp to achieve a uniform color and illuminance distribution on a target architecture surface, which may be a wall or a ceiling. As the illuminance incident on the target decreases as a function of the inverse of the light travelling distance (inverse-square law), the light intensity distribution from the lamp should be highly asymmetric. For example, a fluorescent pendant light which has a symmetric beam shape would illuminate the upper wall much brighter than the lower wall.
Color LED lamps should have an even intensity and color distribution over a broad range of radiation angles. As there is no single point LED source available, the radiation of multiple LED sources must be combined to form a multi-color light source. These multiple LED sources are placed offset to each other, so there is no common focal point. To obtain an even color distribution, color mixing is required.
Another important factor impacting the illumination uniformity is the setback distance, which is defined as the perpendicular distance between the luminaire aperture and the target surface. A small setback distance is usually preferred by lighting and architecture designers, but too short distance may reduce the uniformity, resulting in bright spots on the target plane.
U.S. Pat. No. 8,529,102 discloses a reflector system for a multi-color LED lamp providing color mixing. The system uses two reflective surfaces to redirect the light before it is emitted.
US Publication No. 2007/0171631 discloses LED cove lighting comprising a large and complex aluminum mirror system to obtain a uniform light distribution at a wall.